Gas chromatographic kinetic study of carbon monoxide oxidation over platinum-rhodium alloy catalysts

The kinetics for the oxidation of carbon monoxide in the presence of excess oxygen over Pt-Ph alloy catalysts were studied by using the reversed-flow gas chromatography technique. Suitable mathematical analysis equations were derived by means of which the rate constants for the oxidation reaction of carbon monoxide, as well as for the adsorption and desorption of the react ant CO on the catalysts pure Pt, 75 atom% Pt+25 atom% Ph, 50 atom% Pt+50 at om% Rh, 25 atom% Pt+75 atom% Ph and pure Rh supported on SiO2 were determin ed. All the catalysts show a maximum rate constant for the production of CO 2 at a characteristic temperature close to that found in the literature. Th e rate constants for the adsorption of CO increase generally with increasin g temperature, while those for the desorption decrease with increasing temp erature. From the variation of the rate constants with temperature activati on energies for the oxidation reaction and adsorption of CO were determined , which are sensitive to the composition of the catalytic surface. The appe arance of CO2 and carbon, when introducing pure CO into the column with the catalysts, verified a partial dissociative adsorption (e.g., disproportion ation) of CO on the catalysts used. The latter indicates a mechanism for th e CO oxidation through a partial dissociative adsorption of CO followed by the reaction of adsorbed CO molecules with adsorbed O atoms. (C) 1999 Elsev ier Science B.V. All rights reserved.